Mississippi River bridge collapse in Minneapolis

[Gandalf]

The I-35W bridge (http://customwire.ap.org/dynamic/stories/M/MINNESOTA_BRIDGE_COLLAPSE ?SITE=MOSTP&SECTION=HOME&TEMPLATE=DEFAULT&CTIME=2007-08-01-2) across the Mississippi River collapsed (http://www.foxnews.com/story/0,2933,291790,00.html) during rush hour this evening.

We don't know how many casualties, at present. There are certainly a lot of injuries. And storms are rolling into the area, which could complicate the process of getting people out of the middle of the river.

link to prayer thread (http://thirdday.com/boards/showthread.php?p=1685046# post1685046)

[Kasie_89]

That's horrible. And to know that it could have been prevented.... such a shame.:(

[Gandalf]

And to know that it could have been prevented....
How could we know that? :confused: They haven't determined what caused the failure yet. I would assume it was a fatigue failure, but whether they could've predicted it is another question.

[jrmitch]

How could we know that? :confused: They haven't determined what caused the failure yet. I would assume it was a fatigue failure, but whether they could've predicted it is another question.This hits too close to home. I lived in Minneapolis for 5 years and drove across that bridge every day. God have mercy on all that are involved...........

[Tony Trout]

I just saw this on the news....this is horrible....most definitely praying for all involved....

\O/

[middletree]

http://www.liveleak.com/view?i=1ab_1186054443&p=1

Security camera catches the collapse.

[Kasie_89]

How could we know that?

on the news they have said that the bridge was declared "structurally unsafe". They should have started fixing this bridge alot sooner, and not just surface work.

[mindyhere]

This is so sad. I've been watching the vids on CNN.... :( I have been praying for those yet to be accounted for. I hope that they can be saved.

[Gandalf]

on the news they have said that the bridge was declared "structurally unsafe". They should have started fixing this bridge alot sooner, and not just surface work.
The news of prior inspection results hadn't hit any sources I had access to last night when I asked that. Still, 12% of the bridges across the country are categorized as "structurally deficient" (the actual term used) - that doesn't mean they're necessarily unsafe and in imminent danger of collapsing. It'll be interesting to read the report of the investigation.

[ausgirl]

Last night the reports said 9 dead, this morning it's 4 - so they must have found some, that's good anyway. Praying

[Kasie_89]

Just image all those people who are just waiting to hear if their loved one is alive or dead. It could be days, or weeks even until they are able to look at all the cars underwater.... The news states that over 30 people are still declared missing. It's just so sad.

[jrmitch]

The news of prior inspection results hadn't hit any sources I had access to last night when I asked that. Still, 12% of the bridges across the country are categorized as "structurally deficient" (the actual term used) - that doesn't mean they're necessarily unsafe and in imminent danger of collapsing. It'll be interesting to read the report of the investigation.Just to clarify a little further, one of the things that has come out as a result of this tragedy is that in Minnesota alone there are about 1000 bridges rated in a similar condition and over 10,000 nationally. And he's also right in that structurally deficient doesn't mean in imminent danger of collapse - it just means that the structure is wearing down and will need to eventually be either renovated or replaced. But there was nothing - nothing - in the most recent inspections to indicate that this kind of collapse was even remotely a possibility.

http://www.kare11.com/news/news_article.aspx?storyid =261200

[Pouye]

I'm no engineer, but it seems to me that any bridge of that vintage with such high use could be in danger of collapse. Concrete, even reinforced, does not deal well with decades of vibration and flexing. Unlike buildings, bridges endure much more flexing and changes in stress patterns from uneven and varied distribution of weight. They are also more exposed to the elements (sun, wind, rain, snow, ice, etc.)

The USA's transport system rapidly expanded post WWII, with lots of bridges and more arterials being built. It was a time of building dams and super structures, as well. Many of the bridges built in the 50's and 60's are still in use today, and even though they were generally engineered well, the designers and engineers could hardly account for the continual increase in use (being the up factor) and the deterioration over time (the down factor). As the bridges have grown inherently less stable, the traffic and loading has increased, in other words.

I don't think repair of such a structure is usually a good idea. Such structures tend to wear "entirely" (not just in one aspect or in one little spot). Because of this it is probably better to build new and dismantle the old, in my opinion.

When I looked at the design of that old bridge, I can't say I was very impressed. It appeared to be under supported, with the arched matrix of steel supports undersized for the massive slab of concrete above it. It just seemed really top heavy, with the arches too "flat" to support the surface.

I'm no engineer, but I have played a lot with kapla blocks and legos... :eek:

Rock

ps. Our prayers for the folks who this affected!

[Gandalf]

That bridge was only 40 years old. Major Interstate highway bridges (river bridges, etc. like this one) are usually designed to last 100; at least 75, in any case. Smaller overpasses at intersections are sometimes only designed for 40 or 50. But this bridge should've had another 50 or so years of service, properly maintained, unless there were design flaws that come to light.

The problem was most likely a combination of the design not being robust enough to tolerate deterioration, and poor maintenance, but we'll have to wait for the report to find out. It was almost certainly a failure caused by fatigue cracks propagating in the steel superstructure; the question is whether they missed something in an inspection, or waited too long to repair problems they had detected, or...

[Pouye]

That bridge was only 40 years old. Major Interstate highway bridges (river bridges, etc. like this one) are usually designed to last 100; at least 75, in any case. Smaller overpasses at intersections are sometimes only designed for 40 or 50. But this bridge should've had another 50 or so years of service, properly maintained, unless there were design flaws that come to light.

The problem was most likely a combination of the design not being robust enough to tolerate deterioration, and poor maintenance, but we'll have to wait for the report to find out. It was almost certainly a failure caused by fatigue cracks propagating in the steel superstructure; the question is whether they missed something in an inspection, or waited too long to repair problems they had detected, or...

I'm not saying that it wasn't supposed to last longer, just that 40 years of increased stress and load has a way of teasing out design flaws. The understructure appeared to me to be undersized for the expanse and weight, and I agree that the stress/fatigue on the steel girders was the most likely cause. The concrete appeared to be considerably weakened, which it will be if it is not properly supported. Looking at a couple of aerial photos, it appears that the girders buckled sideways and twisted right out from underneath the structure.

Anyhoo... we'll have to wait for the report, as you say...

Rock

"The problem was most likely a combination of the design not being robust enough to tolerate deterioration, and poor maintenance..." (Yup!)

[Gandalf]

Hopefully, they'll replace it with something a little more attractive, as well as longer-lasting. It's not the steel deck arch truss concept that's flawed - the Eads Bridge (http://en.wikipedia.org/wiki/Eads_Bridge) was the first to use such a design, has longer spans, sits higher off the river, has decks for both rail and road traffic, was finished in 1874, and is still in use today.

Failed I-35W bridge:
http://www.visi.com/~jweeks/bridges/pics/i35wmiss02.jpg

Eads Bridge:
http://de.structurae.de/files/photos/2071/ead_s_auto_and_metrolink_ bridge_august_26_2004.jpg